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*When using the data, please cite the article for which the data were collected for:
*Kemppinen, Niittynen, Virkkala, Happonen, Riihimäki, Aalto & Luoto (Accepted). Dwarf shrubs impact tundra soils: drier, colder, and less organic carbon. Ecosystems.
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Title
Data from: Dwarf shrubs impact tundra soils: drier, colder, and less organic carbon

Data collectors and producers
Kemppinen, Julia; Niittynen, Pekka; Virkkala, Anna-Maria; Happonen, Konsta; Riihimäki, Henri; Aalto, Juha & Miska Luoto

ORCID
Julia Kemppinen 0000-0001-7521-7229
Pekka Niittynen 0000-0002-7290-029X
Anna-Maria Virkkala 0000-0003-4877-2918
Konsta Happonen 0000-0002-3164-8868
Henri Riihimäki 0000-0002-5727-6492
Juha Aalto 0000-0001-6819-4911  	
Miska Luoto 0000-0001-6203-5143

Contact information
julia.kemppinen@gmail.com

Abstract
In the tundra, woody plants are dispersing towards higher latitudes and altitudes due to increasingly favourable climatic conditions. The coverage and height of woody plants are increasing, which may influence the soils of the tundra ecosystem. Here, we use structural equation modelling to analyse 171 study plots and to examine if the coverage and height of woody plants affect the growing-season topsoil moisture and temperature (< 10 cm) as well as soil organic carbon stocks (< 80 cm). In our study setting, we consider the hierarchy of the ecosystem by controlling for other factors, such as topography, wintertime snow depth and the overall plant coverage that potentially influence woody plants and soil properties in this dwarf-shrub dominated landscape in northern Fennoscandia. We found strong links from topography to both vegetation and soil. Further, we found that woody plants influence multiple soil properties: the dominance of woody plants inversely correlated with soil moisture, soil temperature, and soil organic carbon stocks (standardised regression coefficients = -0.39; -0.22; -0.34, respectively), even when controlling for other landscape features. Our results indicate that the dominance of dwarf shrubs may lead to soils that are drier, colder, and contain less organic carbon. Thus, there are multiple mechanisms through which woody plants may influence tundra soils.

Keywords
dwarf shrubs, shrubification, snow, microclimate, carbon cycle, structural equation model, tundra, Arctic

Acknowledgements
We thank all past and present members of the BioGeoClimate Modelling Lab and the Arctic Microbial Ecology group at the University of Helsinki for their assistance during field and laboratory work, and the staff at the Kilpisjärvi Biological Station for their support. The National Land Survey of Finland and the Finnish Meteorological Institute gratefully provided the LiDAR and meteorological data.
 
Funding
JK and HR were funded by the Doctoral Programme in Geosciences at the University of Helsinki. PN was funded by the Kone Foundation. A-MV was funded by Societas pro Fauna et Flora Fennica, the Otto Malm Foundation, and the Väisälä Fund. KH was funded by the Doctoral Programme in Wildlife Biology Research at the University of Helsinki. JA was funded by the Academy of Finland (project no. 307761). Field campaigns were funded by the Academy of Finland (project no. 286950).


Structure of the data
The first column is the site identification number. After which are the four topography variables, namely elevation (m), topographic wetness index (TWI), topographic position index (TPI), and potential incoming solar radiation (kWh/m2). The topography variables are followed by absolute vascular plant species coverage (%), snow depth (cm), woody plant species height (cm), evergreen woody plant species height (cm), deciduous woody plant species height (cm), relative coverage of woody plant species (%), relative coverage of evergreen woody plant species (%) and relative coverage of deciduous woody plant species (%). The three last columns are the soil properties: soil moisture (volumetric water content %), soil temperature (°C) and soil organic carbon stock. For a detailed description on the data, please see Kemppinen et al. (Accepted).

Copyright
This work is licensed under a CC0 1.0 Universal (CC0 1.0) Public Domain Dedication license.